The present invention relates to a decoding device, a decoding method and a decoding program for detecting falsification of an image.
A method of embedding a code into an image is exemplified by a method of segmenting the image on a block-by-block basis and embedding the code on the basis of a relationship between level magnitudes of pixel values of neighboring blocks. Further, a decoding method of extracting the code embedded into the image is exemplified by a method (as given in, e.g., Patent document 1) of previously embedding the same code so as to be repeated a plural number of times and deciding the code exhibiting a highest frequency in the plurality of codes extracted from the image on the basis of a decision by a majority. According to this method, even if a partial error exists in the extracted code, a correct code can be acquired. This is based on such an idea that if there are a large number of correct codes even when the extracted codes are partially erroneous, the correct code can be acquired based on the decision by the majority.
[Patent document 1] Japanese Patent Application Laid-Open Publication No. 2004-349879